Don Knotts, the TV, film and stage actor who capitalized on a persona of the nervous, bumbling boob, died Feb. 24 at the age of 81.

Mr. Knotts was widely known as nervous, fumbling Deputy Barney Fife on TV's "The Andy Griffith Show" in the 1960s. He also played Mr. Furley, the leisure-suit-wearing, middle-aged Romeo landlord on "Three's Company" 1979-84.

Mr. Knotts and Andy Griffith appeared together in the 1955 Broadway comedy No Time for Sergeants and their association led to Mr. Knotts being cast in the role of deputy to Griffith's Sheriff Andy Taylor in the "Andy Griffith" sitcom set in small-town Mayberry, NC. Griffith said on the "Today" show Feb. 27 that in real life Mr. Knotts was nothing like the fretting, shaky characters he created. He also credited the actor with improvising his own lines that gave the classic series an extra comic kick.

Sergeants was Mr. Knotts' only Broadway credit, but he appeared in national tours of comedies and in many summer stock productions over the years. In the 1990s, he starred in a national tour of Neil Simon's The Last of the Red Hot Lovers.

The cause of death was pulmonary and respiratory complications at U.C.L.A. Medical Center in Beverly Hills, according to a spokesman for the cable network TV Land, which broadcasts "The Andy Griffith Show" and "Three's Company" in re-runs.

Mr. Knotts was a five-time Emmy Award winner for his work in "The Andy Griffith Show." He also appeared on lifelong pal Griffith's "Matlock" series. His family-friendly film work included 1964's "The Incredible Mr. Limpet," in which he played a Navy reject who fell off a pier and was transformed into an animated fish. Mr. Limpet ultimately falls in love with a lady fish and helps destroy enemy ships during World War II.

Other film credits include "Pleasantville," "It's A Mad, Mad, Mad, Mad World," "The Ghost and Mr. Chicken," "The Shakiest Gun in the West," "No Deposit, No Return," "The Apple Dumpling Gang," "Gus" and "Herbie Goes to Monte Carlo."

Mr. Knotts was native of West Virginia, where he was a speech major at West Virginia University. In 1998, a street was named after him in his hometown, Morgantown.